Abstract: The method of the thermal design for infrared earth sensors mounted outside the GEO satellite is presented, and a thermal ma|thematical model is built. Based on the sensitivity analysis of the influencing factors, the design scheme is optimized. Results she that the scheme call satisfy the requirements of the working temperature of the sensors during the 15a life cycle of the satellite. This design method has already been applied to the DFH-4 platform series satellites successfully, and be verified in the orbit.